This invention relates to a method and apparatus for handling newly formed glass articles, and, more particularly, the subject invention concerns a novel manipulative process and apparatus for carrying or conveying lightweight containers immediately following their formation so that their pristine characteristics are preserved yet still allowing for further embodiment, including annealing.
There have been substantial efforts of late in the glass industry to make glass containers with thinner sidewalls in order to render them lighter in weight and, therefore, more economical in their production. Because the walls are thinner, such lightweight glass containers are more prone to breakage or fracture. Thus, there have been investigations to find suitable means to strengthen these containers while allowing cost savings through the use of thinner walls. Although such lightweight glass containers my be readily produced by the conventional processes by carefully controlling the molten glass gob introduction, the molding technique and the like, such glass containers cannot be commercially used employing the state of the art equipment and processes since the containers so processed suffer easy breakage or fracture.
As is known, the tensile strength of perfect glass is exceedingly high, if the surface of the glass is completely unabraded. That is, the intrinsic strength of glass may be, for example, more than 7,000 Kg/cm.sup.2 in a nonscratched or unabraded state, the so-called original or pristine glass state, but, when the surface is checked or bruised, its strength is substantially lowered, for example, to about 200 Kg/cm.sup.2. When glass articles are conveyed by conventional equipment such as when newly formed glassware articles are transported en masse on a conveyor belt through an annealing lehr, the glassware articles are not only being abraded by such a conveyor means on the contacting points or surfaces thereof, but the glassware articles themselves are abraded in making contact with each other and thus are checked or bruised whereby their strength is lowered to a marked degree.
In the manufacture of glass articles such as containers by conventional practices, molten glass issuing from a furnace is formed by either press-and-blow or blow-and-blow processes and is then transferred while still hot to a conveyor whence the containers are subsequently transferred into an annealing lehr. While the containers are at an elevated temperature and being handled on conveyors and transfer equipment including pusher-bars and the like, the glass surfaces remain extremely susceptible to damage by merely contacting any hard or abrasive surface. A major reason for this is that the glass articles in cooling do so faster at the exterior surface than at the interior and therefore the exterior surface or skin of said articles is in a state of tension like a stretched rubber band and is highly susceptible to damage while in that condition. Thus, in making contact with any hard surface the skin may be readily ruptured.
In transferring glass containers various conveying devices are conventionally used. In this regard it is exceedingly difficult, if not impossible, to deliver newly formed glassware articles while still very hot without exposing them to some degree of deformation, abrasion or fracture during the transferring operation. Likewise, each point of contact could cause loss or damage due to hot glass surfaces contacting one another and sticking together. Moreover, to those familiar with the manufacture of glass containers, it will be appreciated that the normal methods employed to transfer containers not only subject the glass surfaces to severe contact damage as described but also cause loss thereof due to upsets where scores of containers fall and break during their travel in conventional processing and handling.
Various proposals have hitherto been made in order to protect glass articles from scratching or bruising and to improve the strength thereof. The present invention is intended to maintain the pristine state of glass by providing means to avoid the formation of substantial defects including flaws, checks or microcracks on the surfaces of glass articles, such defects being responsible for the failure of glass articles under load. In effect, the subject invention relates to a method of avoiding or substantially reducing the formation of the aforementioned defects by using a novel manipulative process for handling newly formed glass articles, especially lightweight glass containers.
U.S. Pat. No. 3,392,006 to Seymour describes a glass gripping tong device whereby glass articles are suspended such as glass sheet during thermal treatment, tempering, coating and press bending. U.S. Pat. No. 3,559,425 to Irwin, et al., teaches a glassware takeout device which grasps the neck portion of a container and moves it without touching its bottom to a moving conveyor. U.S. Pat. No. 3,615,327 to McLary discloses a method of coating glass containers while being suspended and conveyed along a given path of movement. Further U.S. Pat. No. 3,765,856 to Bowman discloses a method of engaging bottles at their finish or neck and lifting them from one movable support to another out of contact with each other. Further, U.S. Pat. No. 3,764,284 to Rowe discloses a method of treating newly formed glassware while being suspended so as to expose the base portion to cooling fluids or a metallic chloride spray. Again, U.S. Pat. No. 3,846,101 to Gaskell, et al., discloses thermally crystallizing a ceramic article while being supported in a vertical attitude. The article is suspendingly supported with its major axis or plane of symmetry extending downwardly during the heating step to obtain crystallization. Lastly, U.S. Pat. No. 3,934,993 to Bowman, et al., discloses a glassware handling and treating device for bottles by gripping and suspending them from a conveyor means and passing them over a heating zone, a cooling zone and drying zone for removing surface irregularities.